MOLECULAR RECONSTRUCTION AND HOMOLOGY MODELING OF THE CATALYTIC DOMAIN OF THE COMMON ANCESTOR OF THE HEMOSTATIC VITAMIN-K-DEPENDENT SERINE PROTEINASES

The vitamin-K-dependent serine proteinases of coagulation have evolved by a process of gene duplication and divergence, acquiring along the way a considerable degree of functional diversity that has equipped th em for their different roles in haemostasis. The cDNA sequences encodi ng the catalytic domains of the early mammalian ancestors of five vita min-K-dependent factors (factors VII, IX and X, protein C and prothrom bin) were reconstructed by employing cDNA sequence data from a range o f extant mammals and by using established phylogenies. The cDNA sequen ce of the putative common ancestor of these early mammalian proteins w as then reconstructed from the five sequences by using a deduced phylo geny that was different in a number of respects from those previously proposed. Factor IX is proposed to have branched off early on, followe d by protein C and prothrombin and finally factors VII and X. Signific ant differences in mutation rates were observed between proteins withi n a species; factor IX exhibited a lower mutation rate than the other proteins, consistent with its early emergence. Differences in mutation rates were also observed between species for a given protein and thes e exhibited an inverse con-elation with generation time. A biophysical ly plausible structure for the ancestral vitamin-K-dependent factor pr otein was constructed by comparative methods. Studies of the functiona l architecture of this model provide new insights into the evolution o f protein-binding specificity in this family of proteins.